The present invention relates to thermally developable photothermographic materials and a processing method thereof.
Plate-making work has undergone remarkable changes from manual work to electronic stripping. In such a trend, plotters such as an image setter have rapidly come into wide use. A processing machine for conventional silver salt photographic materials is connected on line to such a precision instrument, producing problems that gas or moisture from the processing solution causes the substrate to corrode, resulting in an increase of troubles in expensive instruments.
In conventional silver salt photographic materials, water supply piping is needed for dilution of developer and fixer solutions as well as washing and recovery of processing effluents by dealers requires much time and labor.
A dry processing system without using water is expected from such a background. Among various dry processing systems, thermal processing is most suitable for practical use in terms of manufacturing cost and performance. However, photothermographic materials are sensitive to variations of temperature in the thermal processing section. Maintaining a uniform temperature of the heated drum surface leads to enhanced quality of finished prints, as is disclosed in JP-A 9-297384 and 9-297385 (hereinafter, the term, JP-A refers to an examined and published Japanese Patent Application).
In this technique, however, maintaining a uniform surface temperature of the drum results in non-uniformity in thermal expansion or shrinkage of the photographic material, leading to the distorted photographic material after thermal processing and producing a problem that moirxc3xa9 images tend to occur after thermal processing, which are not suited to the use for plate-making. Specifically, in cases when used in color printing, such a problem is marked.
Thermal plastic resin, specifically, polyethylene terephthalate (also simply denoted as PET) is employed as a support material for photothermographic materials, in terms of low cost and superior film-making property. However, the use of such a support often causes moirxc3xa9. The glass transition point (Tg) of such a resin is ca. 80xc2x0 C. and the photothermographic materials are thermally processed usually at a temperature of 100xc2x0 C. or higher. It is assumed that such moirxc3xa9 is caused by deformation of the photographic material accompanied with shrinkage or elongation of the support. Thus, it is contemplated that deteriorated dimensional stability causes moirxc3xa9 images. To enhance dimensional stability, it has been attempted to improve thermal variation of the ratio of the dimension in the winding direction to that in the width direction (MD/TD) in the course of preparing the support, e.g., as disclosed in JP-A 10-10676 and 10-10677. However, there was not obtained sufficiently satisfactory stability only by such a technique.
As a result of the inventors"" study, it was proved that deformation caused by distortion markedly affects dimensional stability and that the distortion (or deformation) of a support could not be definitely determined by taking the distance between two points corresponding to the perpendicular direction and the parallel direction to the width of the film support. When a support such as PET base is subjected to biaxial stretching in the preparation thereof, for example, the MD direction is cooled and fixed while being stretched. When developed at a temperature higher than the glass transition point (Tg), the support is softened and tends to shrink in the MD direction and elongate in the TD direction. There have been known a trial of reducing the thermal dimensional change in the MD and TD directions, as afore-mentioned. However, superior quality print images cannot be obtained by only such a technique. In cases when deformed in such a manner as shown in FIG. 1-2, for example, although no dimensional change occurs in either the MD or the TD direction, the square still is deformed, i.e., distortion is caused. The fact that the dimensional change (MD/TD) is small but the printed images are nevertheless inferior is presumed to be due to occurrence of the distortion described above. The thus produced distortion appears as a phenomenon of so-called moirxc3xa9, resulting in deterioration of printed images. Thus, the present invention was achieved based on noting that the dimensional stability of the photothermographic material could not be enhanced to sufficiently satisfactory levels without improvements not only in the MD/TD but also in the distortion of the photothermographic material.
It is an object of the present invention to improve distortion of the photothermographic material. It was proved that when the distortion was represented as an angle and the difference in angle between before and after being processed with respect to three corners of the square being within 0.03xc2x0, deterioration of printed images was not visually detected.
It was noted that achievement of holding the distortion of the photothermographic material to within 0.03 degree includes an approach of devising installation of heaters or a heating procedure in a thermal processing apparatus, and an approach of improving the photothermographic material itself, whereby improvements of a thermal processing apparatus, a thermal processing method and a photothermographic material were accomplished. It was further proved that in the case of improving the photothermographic material, an improvement in the support largely affected the distortion angle and improvement in an image forming layer or a constituting layer also affected the distortion angle.
When angles at three corners of a 10 cm square, as shown in (a), (b) and (c) of FIG. 1 are measured before and after being thermally processed, the distortion defined in this invention refers to the maximum of the values at the three corners with respect to the difference in angle between before and after being thermally processed. The distortion can be determined in such a manner that 10 cm squares are measured as many as possible, in the width direction of the photothermographic material (preferably, in the perpendicular direction to the transport direction of the photothermographic material in the thermal processing apparatus, and more preferably in the width direction of the support roll; herein), and judgment is made based on whether the distortion is within 0.03xc2x0 or not. In the case of 590 mm of the width of a photothermographic material, for example, five pieces of a 10 cm square are cut from the width direction of the unprocessed photothermographic material. With regard to each of these squares, the difference in angle between before and after being thermally processed, at the three corners (i.e., a, b and c) is within 0.03xc2x0 (and preferably within 0.017xc2x0). Since fluctuation is negligible in the transport direction, there is no need of plural sampling in the transport direction. Herein, the width direction refers to the laterally stretching direction in the biaxial stretching of the support and the transport direction refers to the longitudinally stretching direction.
When 10 cm squares are samples from a few locations within the size of a newspaper sheet and the difference in angle was measured, for example, if no variation in the angle occurs (i.e., in the case of being a similar figure), the overall space is said not to be distorted, though the size of the squares may differ. However, such a case almost never occurs. The distortion occurs non-uniformly so that it can be determined by measuring the angle at each of these three points. FIG. 1-1 illustrates distortion as defined in this invention, in which the variation in angle between before and after being processed may be within 0.03xc2x0 at the three points a, b and c.
Accordingly, it is an object of the present invention to provide photothermographic materials exhibiting improved dimensional stability and no moirxc3xa9 images after being processed, a processing method and a thermal processing apparatus by the use thereof.
The object of the invention can be accomplished by the following constitution:
1. A method for processing a photothermographic material comprising the step of:
subjecting the photothermographic material to heat development by the use of a thermal processing apparatus,
wherein the photothermographic material comprises a support, organic silver salt particles, light sensitive silver halide grains, a reducing agent and a contrast-increasing agent; and after being subjected to heat development, the photothermographic material exhibits a distortion of not more than 0.03 degree;
2. The processing described in 1, wherein the thermal processing apparatus comprises a heat-developing section to heat-develop the photothermographic material, the heat-developing section contains at least three heaters which are independently capable of controlling temperature;
3. The processing method described in 2, wherein the three heaters are arranged in the direction substantially vertical to the transporting direction of the photothermographic material;
4. The processing method described in 1, wherein the thermal processing apparatus further comprises a cooling section to cool the heat-developed photothermographic material, and the cooling section contains at least two coolers which are independently capable of controlling temperature;
5. The processing method described in 4, wherein the two coolers are arranged in the direction substantially vertical to the transporting direction of the photothermographic material;
6. The processing method described in 1, wherein the photothermographic material comprises an image forming layer, the image forming layer comprises the organic silver salt particles, the light sensitive silver halide particles and a binder, and at least 50% by weight of the binder is accounted for by a polymer latex exhibiting a glass transition point of, less than 40xc2x0 C.;
7. The processing method described in 1, wherein the photothermographic material comprises an image forming layer, the image forming layer comprises the organic silver salt particles, the light sensitive silver halide particles and a binder, and at least 50% by weight of the binder is accounted for by a polymer latex exhibiting a glass transition point of not less than 40xc2x0 C.;
8. The processing method described in 1, wherein after subjected to heat development, the photothermographic material exhibits a distortion of not more than 0.017 degree;
9. The processing method described in 1, wherein said support is one which was previously subjected to a thermal treatment at a temperature of 110 to 190xc2x0 C. over a period of 15 to 30 min., while being transported under a tension of 2 to 6 kg/cm2;
10. The processing method described in 9, wherein the photothermographic material comprises an image forming layer; the image forming layer is coated on the support and wound up at a tension of 20 to 60 kg/cm2, and
11. A thermal processing apparatus for heat-developing a photothermographic material comprising a heat-developing section to heat-develop the photothermographic material, the heat developing section having at least three heaters, wherein the three heaters are independently capable of controlling temperature, the three heaters being arranged in the direction substantially vertical to the transporting direction of the photothermographic material;
12. The thermal processing apparatus described in 11, wherein the apparatus further comprises a cooling section to cool the heat-developed photothermographic material, the cooling section having at least two coolers; and the two coolers are independently capable of controlling temperature and being arranged in the direction substantially vertical to the transporting direction of the photothermographic material;
13. A photothermographic material comprising a support, organic silver salt particles, light sensitive silver halide grains, a reducing agent and a contrast-increasing agent, wherein after having been subjected to heat-development by the use of a thermal processing apparatus, the photothermographic material exhibits a distortion of not more than 0.03 degree;
14. The photothermographic material described in 13, wherein the photothermographic material is subjected to heat-development at a temperature of 30 to 150xc2x0 C. in the thermal processing apparatus;
15. The photothermographic material described in 13, wherein the photothermographic material comprises an image forming layer, the image forming layer comprises the organic silver salt particles, the light sensitive silver halide particles and a binder, and at least 50% by weight of the binder is accounted for by a polymer latex exhibiting a glass transition point of less than 40xc2x0 C.;
16. The photothermographic material described in 13, wherein the photothermographic material comprises an image forming layer, the image forming layer comprises the organic silver salt particles, the light sensitive silver halide particles and a binder, and at least 50% by weight of the binder is accounted for by a polymer latex exhibiting a glass transition point of not less than 40xc2x0 C.;
17. The photothermographic material described in 13, wherein said support is one which was previously subjected to a thermal treatment at a temperature of 110 to 190xc2x0 C. over a period of 15 to 30 min., while being transported with applying a tension of 2 to 6 kg/cm2;
18. The photothermographic material described in 13, wherein the photothermographic material comprises an image forming layer, the image forming layer being coated on the support and wound up at a tension of 20 to 60 kg/cm2;
19. The photothermographic material described in 13, wherein after subjected to heat development, the photothermographic material exhibits a distortion of not more than 0.017 degree;
20. A processing method of a photothermographic material comprising a support having thereon organic silver salt particles, light sensitive silver halide grains, a reducing agent and a contrast-increasing agent, wherein the photothermographic material exhibits a distortion of not more than 0.03 degree;
21. The processing method described in 20, wherein a thermal processor having heat sources above and below the transport path has at least three sections per one side which are independently capable of controlling temperature above and below the developing path;
22. The processing method described in 20 or 21, at least two sections independently capable of controlling temperature are provided in the cooling process of cooling of the processor;
23. A method for processing a photothermographic material comprising a support having thereon organic silver salt particles, light sensitive silver halide grains, a reducing agent and a contrast-increasing agent, wherein the photothermographic material exhibits a distortion of not more than 0.03 degree after being processed and a binder contained in an image forming layer of the photothermographic material is mainly comprised of a polymer latex having a glass transition point of not less than 40xc2x0 C.; the photothermographic material is processed by the use of a thermal processor having at least three sections perorle side which are independently capable of controlling temperature above and below the developing path;
24. A method for processing a photothermographic material comprising a support having thereon organic silver salt particles, light sensitive silver halide grains, a reducing agent and a contrast-increasing agent, wherein the photothermographic material exhibits a distortion of not more than 0.03 degree after being processed and a binder contained in an image forming layer of the photothermographic material is mainly comprised of a polymer latex having a glass transition point of not less than 40xc2x0 C.; the photothermographic material is processed by the use of a thermal processor, in which at least two sections independently capable of controlling temperature are provided in the cooling process of cooling of the processor.
25. The method for processing a photothermographic material comprising a support having thereon organic silver salt particles, light sensitive silver halide grains, a reducing agent and a contrast-increasing agent described in any one of
(21) through (24), wherein the photothermographic material exhibits a distortion of not more than 0.017 degree.